Process of abrasively buffing a surface of a paper web



- gloss on a paper or mineral-coated paper surface. thermore, said aqueous United States Patent Office 2,696,151 Patented Dec. 7, 1954 PROCESS OF ABRASIVELY BUFFING A SURFACE OF A PAPER WEB No Drawing. Application DeeemberlZ, 1949, Serial No. 132,636

3 Claims. (CI. 92-68) This invention relates to the production of paper, especially mineral-coated papers including metallic coated papers, having an abrasively buffed, glossy surface.

One of the latest of the few known methods of developing extremely high gloss on a-paper surface, and especially on a mineral-coated paper surface, is that disclosed in U. S. Patent No. 2,349,704 to John W. Clark which patent is owned by the assignee of the present application. According to the Clark process, paper having a smoothed surface is polished by means of a resilient roll in conjunction with a polishing composition comprising fine abrasive powder and sufficient adhesive to make said abrasive powder adhere to the polishing roll. Clarks preferred adhesive is one which also acts as a lubricant. During the ten years or more during which the Clark process has been in commercial use the abrasive composition found most satisfactory for use has been a mixture of abrasive'powder and stearic acid cast into a solid bar which bar is in use rubbed (preferably intermittently rubbed) against the polishing roll to apply thereto a film or coating of abrasive.

Although the Clark process has been in successful operation for several years it has required unremitting watchfulness and very precise control to achieve satisfactory results. It is exceedingly diflicult to ensure continuous uniform application of abrasive from an abrasive bar held against the resilient bufling roll and at the same time to apply only the desired small quantity of abrasive. On the other hand, although intermittent application of abrasive to the buffing roll undoubtedly makes for much easier control of the quantity of abrasive applied, it also unavoidably causes variation in the appearance of a coated paper surfacebutfed under such conditions.

The patent indicates that abrasive powder moistened with water is usable, but suggests that the water may soften the paper surface unduly. By experimentation I have ascertained der can be used to buff paper without softening the surface thereof to an objectionable, or even observable, degree. I also found, however, that an abrasive composition consisting of abrasive powder and water is not as effective in promoting high finish or gloss on paper surfaces as is a stearic acid-abrasive powder composition used under the same conditions.

The present invention provides an aqueous bufling composition comprising water, abrasive powder, and watersoluble adhesive and lubricant, said aqueous butting composition being fully as effective as a stearic-acid-abrasive powder bufiing composition in producing high finislli or urbuffing composition can easily be applied continuously in measured quantity to the bufiing roll whereby there is eliminated one important cause of variation in the finish of paper buffed by a method in which abrasive is applied intermittently. Primarily the butting composition of the present invention comprises finely divided abrasive, water, and water-soluble, normally solid, high molecular-weight, polyethylene glycol. Optionally there may also be included in the composition a .small quantity of humectant material" such for example as a hydroscopic liquid polyhydric alcohol.

There are available commercially grades of solid, watersoluble polyethylene glycol which range in molecular weight from about 1000 to about 6000. While all of these grades are usable according to the invention, those of higher molecular weight are preferred.

The aqueous slurry described above can be picked that an aqueous slurry of abrasive powup by a solid roll which turns in the slurry; it can be removed from said roll by a rotating brush which can in turn transfer the slurry to a rotating bufling roll. The latter roll, of course, is the one which buffs the paper being treated. By regulating the speed of rotation of the first mentioned of the above rolls, that is the solid roll which turns in the abrasive slurry, the quantity of abrasive applied to the bufiing roll can be controlled with nicety. The mechanism described is obviously adapted for continuous application of the abrasive to the bufiing roll.

In the abrasive applying system described, the solid roll dipping in the abrasive slurry may suitably be a metal roll or a rubber covered roll. The rotatable brush may be a bristle brush of hog bristle or synthetic bristle such as nylon. The bufling roll itself may be any resilient roll, and suitably is one made by threading over a central shaft fiuted or pleated discs of canvas or other fabric.

As the abrasive component of the composition, which abrasive component may constitute 33 to 95% by weight of the solids content of the composition, any finely divided abrasive powder such as finely divided oxides of aluminum, chromium, iron, silicon and the like may be used. Powdered silica is very satisfactory for use on white paper because of its lack of staining tendencies. It has been previously mentioned that a mere slurry of abrasive in water is not wholly satisfactory for use in bufling paper in that it produces a finish considerably inferior to that obtainable by use of Clarks mixture of abrasive and stearic acid. If solid polyethylene glycol is dissolved in the slurry in quantity as little as 5% of the weight of abrasive present and the resulting mixture is used to buff paper, the results obtained are very definitely superior to those given by use of a slurry containing only abrasive powder and water. Increasing the proportion of high molecular weightpolyethylene glycol present gives still better results. It may be said that polyethylene glycol may constitute from 67 to 5% by weight of the solids content of the composition, and that the ratio of high molecular weight polyethylene glycol to abrasive powder may vary from .05 to about 2.0, with the middle portion of the range being most generally useful.

The solid polyethylene glycols, especially those of higher molecular weight, have little tendency to be hygroscopic. Hence when aqueous slurries of such solid polyethylene glycol and abrasive powder become dryon the butling roll, for example-the residue may be brittle and tends to produce dust. It has been found, however, that this undesirable tendency can be obviated largely by including in the aqueous slurry of abrasive powder and polyethylene glycol of high molecular weight a small proportion of a humectant or hygroscopic agent which tends to prevent the composition from drying out to a dusty condition. The proportion of hygroscopic agent required depends upon the particular agent chosen as well as the relative humidity of the atmosphere in which it will be used. Generally speaking, it will never amount to more than 15% of the weight of the solids present, and in most cases it will be less than that proportion, 2% often being sufficient.

A typical aqueous butting composition useful according to the invention follows:

The quantity of water present in the bufiin'g composition is not critical. Naturally, enough water must be used to dissolve at least part of the high molecular weight polyethylene glycol present and to keep the abrasive powder moist, but water considerably in excess of that as a humeetant,

' quantity may be present if desired. In general, the composition may be either a paste orv a very thin slurry depending on the preference of the user and on the means .300 ft. per minute.

provided for applying the composition to the resilient polishing roll or bufling-roll.

The invention is an improvement on the invent on of the Clark Patent No. 2,349,704, the improvement residing in the butfing or polishing composition used, its method of application, and the better and more uniform quality of buffed paper surface produced, the purpose being the production of paper (especially mineral-coated paper) having a high degree of gloss. As a preparatory step the surface of a paper web is treated, suitably by means of a supercalender, to render it smooth and level. The so-smoothed surface is then subjected to the polishing or bufiing action of a re'silientroll carrying a layer of the aqueous slurry of abrasive powder and high molecular weight polyethylene glycol previously described.

In general, the primary purpose of bufling a paper surface according to the invention is to increase the glossiness of the surface. The degree of glossiness produced naturally is to some extent dependent upon the composition of the surface being buffed, and upon the treatment to which it has previously been subjected, as well as to the severity of the bufling treatment given.

In the paper trade, gloss of paper is commonly measured by means of the Bausch and Lomb glossmeter by which the reflectance of the surface when both illuminated and viewed at an angle of 75 from the perpendicular is compared to that of a standard glass surface illuminated and viewed under the same conditions. The gloss figure reported is a percentage of the gloss" of the arbitrary gloss standard and is read directly from the scale of the Bausch and Lomb glossmeter.

Although the process of the invention is capable of greatly enhancing the gloss of uncoated papers, its most apparent usefulness is in improving the gloss of mineralcoated papers to produce surfaces having gloss higher than can be obtained by a supercalendering treatment. Most of the best quality supercalendered mineral-coated printing papers give a Bausch and Lomb glossmeter reading of between 65 and 70; a few give a reading of over 70; but none, as far as I am aware, ever give a reading of over 75. Buffing such supercalendered paper may be expected to raise the gloss points or more as read by the Bausch and Lomb glossmeter. In general, any glossy mineral-coated paper that is worth butting will be raised to a gloss of at least 80 and preferably of at least 85 as measured by the Bausch and Lomb glossmeter. In some cases it is possible to reach a gloss of 100 by this treatment.

In a typical instance a paper web of 40 pounds on a x 38" 500 sheet ream basis was coated on one side with 15 pounds dry weight of a coating composition comprising the following constituents:

100 parts fine quality calciumv carbonate 4 parts casein (solubilized by alkali) 13 parts butadiene-styrene copolymer (added in emulsion) 120 parts of water The coated sheet was dried and supercalendered to give a Bausch and Lomb glossmeter reading of 69. The supercalendered sheet was then passed through a buffing machine in which the coated surface was buffed by each of two spaced resilient bufiing rolls to which was continuously supplied a polishing composition of the following composition:

Lbs.

Silica powder 448 Polyethylene glycol, mol. wt. 6000 192 Glycerine 63 Water 1190 Total 1893 The composition was divided between two spaced butfing rolls operating in tandem upon the moving web. For each 1000 sq. ft. of paper surface buffed, 1.17 lbs. of the composition, representing 0.43 lb. of components other than water, were used.

Mineral-coated paper as used herein refers to a paper product bearing a surface-coating deposited from aqueous medium and comprising a major pigment component containing a mineral pigment such as clay, calcium carbonate, titanium dioxide, powdered metal, metal flake, or the like, and a minor adhesive component containing an organic binding material such as glue, casein, starch, synthetic elastomer, or the like. Mineral-coated papers, as a group, are amenable to gloss-improvement by being abrasively buffed in accordance with the herein described procedure using the buffing composition described and claimed herein.

I claim:

1. Process of abrasively balling a surface of a paper I web, which comprises continuously advancing a paper 57.2 parts abrasive powder (commercial silica grade O) The paper passed through the machine at a speed of The polishing rolls held a surface speed of about 3000 feet per minute in the direction of paper travel. The paper so treated gave a Bausch and Lomb glossmeter reading of 90.

While no critical limits can be set as to the amount of polishing composition to be used in abrasively buffing a unit area of paper surface, the following will be indicative: In a 4-day run a total of 29,420 pounds of oneside coated 60 pound paper, having a total bulfed surface of approximately 1,618,000 sq. ft., were buffed using a buffing composition composed of the following ingredients:

web, contacting a surface of said moving web with the surface of a resilient butfing roll rotating at a surface speed different from that of the paper travel, and continuously applying to the surface of said rotating resilient buffing roll a metered quantity of an aqueous slurry the solids content of which consists essentially of from 33 to by weight of abrasive powder and from 67 to 5% by weight of water-soluble, normally solid, polyethylene glycol having a molecular weight of from about 1000 to about 6000.

2. Process of abrasively bufiing a surface of a paper web, which comprises continuously advancing a paper web, contacting a surface of said moving web with the surface of a resilient buffing roll rotating at a surface speed different from that of the paper travel, and continuously applying to the surface of said rotating resilient bufiing roll a metered quantity of a liquid slurry consisting of a solids component consisting essentially of from 33 to 95% by weight of fine abrasive powder and from 67 to 5% by weight of a water-soluble, normally solid polyethylene glycol having a molecular weight as high as 1000 but not higher than 6000, and a liquid component consisting essentially of water containing dissolved therein a humectant in an amount corresponding to from about 2 to about 15% by weight of the solids component of the liquid slurry.

3. In the process of abrasively bufiing a surface of a continuously advancing paper web with an abrasive-carrying resilient-buffing roll rotating at a surface speed different from that of the paper travel, the improvement which consists in continuously applying over the bulfing roll surface in metered quantity an even layer of an aqueous slurry the solids content of which consists essentially of from 33 to 95% by weight of abrasive powder and from 67 to 5% by weight of water-soluble, normally solid, polyethylene glycol having a molecular weight of from about 1000 to about 6000, the aqueous component of the slurry being present in a minimal amount sufiicient to dissolve at least a part of the polyethylene glycol and to keep the abrasive powder moist.

References Cited in the file of this patent ate 12, 1942 

1. PROCESS OF ABRASIVELY BUFFING A SURFACE OF A PAPER WEB, WHICH COMPRISES CONTINUOUSLY ADVANCING A PAPER WEB, CONTACTING A SURFACE OF SAID MOVING WEB WITH THE SURFACE OF A RESILIENT BUFFING ROLL ROTATING AT A SURFACE SPEED DIFFERENT FROM THAT OF THE PAPER TRAVEL, AND CONTINUOUSLY APPLYING TO THE SURFACE OF SAID ROTATING RESILIENT BUFFING ROLL A METERED QUANTITY OF AN AQUEOUS SLURRY THE SOLIDS CONTENT OF WHICH CONSISTS ESSENTIALLY OF FROM 33 TO 95% BY WEIGHT OF ABRASIVE POWDER AND FROM 67 AOT 5% BY WEIGHT OF WATER-SOLUBLE, NORMALLY SOLID, POLYETHYLENE GLYCOL HAVING A MOLECULAR WEIGHT OF FROM ABOUT 1000 TO ABOUT
 6000. 